Patent Document 1, for example, discloses the type of lens barrel device. The Patent Document 1 discloses a lens barrel device that includes a plurality of movable lens. A lens barrel device disclosed in the Patent Document 1 is characterized in that “a lens barrel device includes a stationary barrel, a movable barrel moving in the optical axis direction, and a lens frame moving in the optical axis direction interlocked with the movable barrel, the stationary barrel includes a first cam inwardly protruded from an inner circumferential surface thereof, the movable barrel includes an opening portion including a second cam surface facing in the circumferential direction with a predetermined angle, and that the lens frame includes a plurality of cam followers engaged with the first cam in the circumferential direction, with the cam followers being engaged with the second cam at end portions in the circumferential direction”.
According to the lens barrel device having the above configuration, it is expected that “since a structure to move a lens group used in the lens barrel can be achieved by decreasing the number of parts produced with integral molding of resin, an inexpensive lens barrel device can be produced with excellent assembly efficiency”.
Further, Patent Document 2, for example, discloses another lens barrel device of this kind. The Patent Document 2 discloses a lens barrel device that can be used for a lens system of a video camera, or the like. The lens barrel device disclosed in the Patent Document 2 is characterized by “a lens barrel device, a lens disposed within the lens barrel device, a holding means for holding the lens, in which the holding means including a coil, a yoke disposed within the lens barrel device in response to the circumference of the holding means, a magnet disposed within the yoke to move the holding means within the lens barrel device, the magnet forming a linear actuator with the coil when the coil is conducted and a guide means for guiding the holding means of the lens along the lens barrel device by driving the linear actuator, the guide means located at the position inner side of the yoke, the magnet, and the coil in the radial direction”.
According to the lens barrel device having the above configuration, it is expected that “external form of the lens barrel device can be simplified without externally providing the guide means of a guide shaft”.
However, in the above-mentioned lens barrel device described in the Patent Document 1, while cam pins provided on a plurality of movable barrels holding respective lens groups are engaged with a plurality of cam grooves on a cam cylinder and allow the cam pins are caused to move along the respective cam grooves by rotating the cam cylinder, and thereby the movable barrel is caused to move in the optical axis direction; if the number of lens groups is increased, the number of barrels should increase to fit the lens groups into the respective barrels; thus, the lens barrel device will have complicated configuration since an external diameter of an entire lens barrel device increases. In addition, an optical design for lenses and mechanical design for as cam grooves should be compatible with one another, so that parts usually have complicated designs.
Moreover, when the lens barrel device received impact from the front thereof, such impact is immediately transmitted to the cam pins, so that the cam pins may be broken or disengaged from the cam grooves, or the grooves may collide with peripheral parts. Accordingly, the barrel holding the lens group may not move, or peripheral parts may be damaged. In addition, it may be difficult to secure impact-resistance against the lens barrel device.
Further, since the lens barrel device including numeral lens groups to move needs contact slide portions having the cam pins and the cam grooves, so that a large rotational torque is required to drive the lens barrel device; when the lens barrel device is driven, a motor of large torque is generally decelerated gear to rotate. However, if a large-sized motor and a gear box for decelerating gear are mounted on the lens barrel device, the lens barrel device may increase in size.
Moreover, in the lens barrel device disclosed in the Patent Document 2, while the linear actuator is driven to move a plurality of lens frames along the guide shafts in the optical axis direction, backlash may be observed between holes into which the guide shafts of a plurality of lens frames are inserted and the guide shafts, due to dimensional errors of respective parts such as lens frames and errors of mounting accuracy of parts. As a result, adjusting to eliminate backlash without affecting the control of lenses may be required, thereby decreasing operating efficiency.
Patent Document 1:
The Official Gazette of Unexamined Published Japanese Patent Application No. Hei-7-294793
Patent Document 2:
The Official Gazette of Unexamined Published Japanese Patent Application No. Hei-8-15593
The problem to be solved is that, when the cam grooves formed on the cam cylinder are engaged with the cam pins provided on the barrel holding the lens group, and the barrel holding the lens group is moved by rotating the cam cylinder, if the number of lens group is increases, the number of barrels should also increase to fit the lens groups into the barrels, so that the lens barrel device will have a complex design, and the external diameter of the lens barrel device will increase. Further, if the guide shafts support a plurality of lens frames such that the lens frames can move, backlash will be observed between the guide shafts and the guide holes of the lens frames. Accordingly, adjusting to eliminate backlash may be required, thereby decreasing operating efficiency.